Gerald Cavendish Grosvenor, 64, who inherited the title of Duke from his father in 1979 and is among the top 100 richest people in the world, died at the Royal Preston Hospital in Lancashire on Tuesday.

"He was taken there [Royal Preston Hospital] from the Abbeystead Estate in Lancashire where he had suddenly been taken ill. His family are all aware and they ask for privacy and understanding at this very difficult time," a spokesperson for his estate said.

The former Duke was the richest property developer in the UK through his company the Grosvenor Estates, which owns land in Oxford, Cheshire and Scotland as well as vast swathes of property in central London.

His estate includes land in Belgravia, an area adjacent to Buckingham Palace and one of London's most expensive boroughs, as well as thousands of acres in Spain.

He was a close friend of Britain s royal family and Prince Charles and wife Duchess of Cornwall were said to be "deeply shocked and greatly saddened" by the sudden death.

"I can confirm that Her Majesty the Queen is aware of the news about the Duke of Westminster. A private message of condolence is being sent by the Queen and the Duke of Edinburgh," a Buckingham Palace spokesperson said.

The death means the duke's 25-year-old son Hugh has now inherited the estate and title worth 9 billion pounds.

Hugh Richard Louis Grosvenor, previously known by the honorary title Earl Grosvenor, works as an account manager for bio-bean, a green technology company.

He is the godfather of Prince George, the 3-year-old son of Prince William and Kate Middleton and third in line to Britain s throne.

His father had credited himself with using his wealth responsibly and gave financial support to both rural and inner-city areas with links to his estate.

The Westminster Foundation, which manages the estate's charitable giving, has donated to more than 1,500 charitable organisations since 1974.